The present invention relates generally to a bearing surface for a joint and more specifically to a bearing surface for a thin-walled tube utilized with a support linkage for an agricultural implement.
Many farm implements, for example, row crop cultivators, typically include an elongated fore-and-aft extending link pivotally connected at one end to a frame-supported mounting bracket and at the opposite end to coupler plates which support a tool-carrying rig beam. Usually two links are spaced vertically to form four-bar linkage structure with the mounting bracket and coupler plates so that the rig beam remains in a preselected angle with respect to the ground as the tools penetrate the soil and as the links are pivoted up from the field-working position to the transport position. The links are commonly fabricated from solid metal bars and are pinned between the bracket and plates by pivots such as bolts or the like. The bars are not only heavy, but are also relatively thin, and any looseness or play in the pivots results in undesirable side sway of the rig beam and tools connected thereto. The coupler plates must be tight enough against the bars to prevent excessive side movement, but must also be loose enough to permit the rig beam to be raised and lowered and to float with the ground level when a gauge wheel is utilized.
Recently, hollow tubular links which are wider and lighter than the solid bars have been employed with many implements to reduce weight and side sway. The tubular links have a rectangular or square cross section with upright sidewalls which are relatively thin compared to the overall width of the tube. Heretofore, it has been necessary to drill axially aligned holes in the opposite sidewalls and weld a bushing in place between the sidewalls to support each pivot. Long bushings extend from wall to wall, and fabrication of each pivot area requires two welding steps including one for each wall. Once the bushing is welded in place, it is difficult or impossible to replace if it becomes worn or damaged. A complete link assembly often has to be replaced if one bushing is damaged, and the links are relatively expensive because of the bushings and the labor required for fabrication. Additional replaceable wear bushings have been utilized within the welded bushings, but the additional components add cost and increase the time required to fabricate the assembly. Any play between the bushings and the pivot pin, which may be caused by wear or by an improper fit of one or more of the components, may easily cause a side sway problem.